import Data.List (sort)
import qualified Data.IntMap as M

main = interact $ show . solve . map (map read . words) . lines

solve ([n,k]:xs) = ans
    where
        xxs = reverse . sort $ xs
        ans = M.foldl max 0 . foldl f M.empty $ xxs
        f m [p, d] = M.insertWith max (-p) d mm where
            mm = M.foldlWithKey g m m
            g w e c
                | e > 0 && (p + e) <= k = M.insertWith max (-(p + e)) (c + d) w
                | e < 0 = M.insertWith max (-e) (c + d) w
                | otherwise = w